One of the various approaches to immunising against N.meningitidis infection is to use outer membrane vesicles (OMVs). An efficacious OMV vaccine against serogroup B has been produced by the Norwegian National Institute of Public Health [e.g. ref. 1] but, although this vaccine is safe and prevents MenB disease, its efficacy is limited to the homologous strain used to make the vaccine.
The ‘RIVM’ vaccine is based on OMVs containing six different PorA subtypes. It has been shown to be immunogenic in children in phase II clinical trials [2].
Reference 3 discloses a vaccine against different pathogenic serotypes of serogroup B meningococcus based on OMVs which retain a protein complex of 65-kDa. Reference 4 discloses a vaccine comprising OMVs from genetically-engineered meningococcal strains, with the OMVs comprising at least one Class I outer-membrane protein (OMP) but not comprising a Class 2/3 OMP. Reference 5 discloses OMVs comprising OMPs which have mutations in their surface loops and OMVs comprising derivatives of meningococcal lipopolysaccharide (LPS).
As well as serogroup B N.meningitidis, vesicles have been prepared for other bacteria. Reference 6 discloses a process for preparing OMV-based vaccines for serogroup A meningococcus. References 7 and 8 disclose vesicles from N.gonorrhoeae. Reference 9 discloses vesicle preparations from N.lactamica. Vesicles have also been prepared from Moraxella catarrhalis [10, 11], Shigella flexneri [12, 13], Pseudomonas aeruginosa [12, 13], Porphyromonas gingivals [14], Treponema pallidum [15], Haemophilus influenzae [16 & 21] and Helicobacter pylori [17].
The failure of OMVs to elicit cross-protection against non-homologous strains is not well understood, particularly as most N.meningitidis isolates share a small number of conserved protective surface antigens that, if present in OMVs, would be expected to provide broad protective coverage. One possible explanation for the failure is the existence of variable immune-dominant surface antigens that prevent the conserved antigens from exerting their protective action, and the presence of immune-dominant hyper-variable proteins such as PorA has been extensively documented and demonstrated. Other possible explanations are that the methods for OMV preparation result in contamination with cytoplasmic and/or inner membrane proteins that dilute the protective outer membrane proteins, or that antigens are lost by the detergent extraction.
There have been various proposals to improve OMV efficacy. Reference 18 discloses compositions comprising OMVs supplemented with transferrin binding proteins (e.g. TbpA and TbpB) and/or Cn,Zn-superoxide dismutase. Reference 19 discloses compositions comprising OMVs supplemented by various proteins. Reference 20 discloses preparations of membrane vesicles obtained from N.meningitidis with a modified fur gene. Reference 21 teaches that nspA expression should be up-regulated with concomitant porA and cps knockout. Further knockout mutants of N.meningitidis for OMV production are disclosed in references 21 to 23. In contrast to these attempts to improve OMVs by changing expression patterns, reference 24 focuses on changing the methods for OMV preparation, and teaches that antigens such as NspA can be retained during vesicle extraction by avoiding the use of detergents such as deoxycholate.
It is an object of the invention to provide further and improved vesicle preparations, together with processes for their manufacture. In particular, it is an object of the invention to provide vesicles which retain important bacterial immunogenic components from N.meningitidis. 